With the ongoing retirement of the Boeing 747-400 and the end of production of the Airbus A380, there is no doubt four-engine aircraft are falling out of favor. Twin-engine aircraft have improved significantly, and many airlines are moving away from the high-capacity ‘hub and spoke’ model. It seems unlikely there will be a need anytime soon for a four-engine passenger aircraft, but perhaps it could re-appear for freight. //

Four engine production has declined as twin-engine operations have improved. In the early days of jet aircraft, a twin-engine aircraft (under FAA rules) could not fly more than 60 minutes away from a diversion airport. This hugely limited the possibilities for trans-oceanic flights. //

Along with this improvement in ETOPS, engine power has also increased. A 1958 Pratt & Whitney JT3D engine on the 707, for example, had a thrust of 17,000 pounds, versus the GE9X engine on the 777X with around 105,000 pounds of thrust. Manufacturers can now power large single-deck widebodies with two engines.